Water insoluble algin fibers have been produced by spinning or extruding water soluble algin solutions into a coagulating bath which is composed of an aqueous solution of multivalent metal ions. When a coagulating bath contains copper or calcium ions, water insoluble copper or calcium algin fibers are obtained, respectively, as disclosed in Japanese Patent Laid-open No. 56-169809, Europian Patent application No. 0 040 048 or U.S. Pat. No. 3,446,625. The alginates have haemostatic properties, and therefore fabrics of such algin fibers are used as swabs or dressings and the like suitable for medical, surgical and other purposes.
There are disclosed in British Patent No. 1,231,506 water solubilized alginate calcium/sodium fibers which are produced by acidifying water insoluble alginate calcium fibers and then treating the acidified fibers with an alcoholic solution of sodium hydroxide. Also in European Patent Application No. 0 040 048, there is disclosed a process for the production of nonwoven fabrics of calcium/sodium alginate fibers by acidifying calcium alginate fibers with acetic acid to displace in part calcium ions with sodium ions and then treating the fibers with an alcoholic solution of sodium acetate.
There is further disclosed in Japanese Patent Publication No. 27720/1989 a process wherein water insoluble alginate calcium is extruded into a coagulating bath together with enzymes or microorganisms to produce water insoluble alginate fibers which have thus the enzymes or microorganisms immobilized thereto useful as a bioreactor.
As above described, water insoluble alginate fibers are already known. It is also known that an alginate powder is obtained by adding hydrophilic organic nonsolvent to an aqueous solution of water soluble algin. However, no process has hitherto been known for the production of substantially Hater soluble algin fibers on account of a high solubility of sodium alginate in water in contrast to calcium alginate which is very slightly soluble in water. More specifically, the extrusion of an aqueous solution of water soluble algin or a dope into a nonsolvent in which water algin is insoluble fails to provide continuous filaments of the water soluble algin in a stable manner because of a high compatibility of the water soluble algin to water.